1. Field of the Invention
The present invention relates to capacitors capable of being mounted on printed circuit boards by means of soldering, and a method for manufacturing such capacitors.
2. Description of the Prior Art
Capacitors which are in the form of individual components for mounting by soldering on a printed circuit board must resist the influences of the solder fluxing agent, the hot liquid solder, as well as chemical liquid cleaning agents without damage to the capacitor itself.
Capacitors are known in the art having a stacked or layered construction or a flat-pressed winding, with the layers having coatings on the large faces thereof which respectively terminate at opposite end faces of the capacitor stack or winding with a metal plated layer being electrically conductively connected to the coatings at each of the end faces. Current leads are electrically and mechanically connected to the metal platings. Such a stacked or layered capacitor is described, for example, in German Pat. No. 1,764,541, corresponding to U.S. Pat. Nos. 3,670,378 and 3,728,765.
Other types of capacitors are also known consisting of a sintered member, such as a tantalum sinter capacitor, those capacitors also having metal elements disposed at opposite end faces for connecting to current leads. Generally the tantalum sinter element is porous and has coatings on opposite sides thereof consisting of conductive metal oxides, these coatings being generated during the individual manufacturing steps for the capacitor.
Ceramic multi-layer capacitors are also known such as described, for example, in the U.S. Pat. No. 3,740,624, consisting of alternating ceramic and metal layers, with the metal layers being guided to opposite end faces of the capacitors and being electrically connected at the end faces by means of metal plating.
A problem in the use of such capacitors, particular capacitors of the type described above having dielectric material consisting of plastic, is the sensitivity of such capacitors to the influence of fluxing agents, hot liquid solder, and liquid chemical cleaning agents. Plastics commonly utilized as dielectric material in capacitors are, for example, polyethylene terephthalate, polycarbonate, polypropylene, cellulose acetate, and the like. Capacitors having a ceramic dielectric element or a tantalum sinter member are also subject to being damaged during the mounting of such capacitors as chip components on a printed circuit board. For example, by the influence of the heat accompanying the application of solder, the dielectric properties can change in an unfavorable manner, and the chemical influence of the fluxing agent and/or of cleaning agents may also adversely affect such capacitors.
In order to minimize the influence of such disturbances, many electronic components, including capacitors, are contained in housings or envelopes which provide a certain immunization from such influences, making those components suitable for utilization as chip components. Generally when attaching such components to a printed circuit board, solder is employed which, in the liquid state, exhibits temperatures up to 260.degree. C., and the soldering operation lasts approximately 10 seconds.
A capacitor is described in German Pat. No. 3,120,298 in chip component construction which includes a capacitor member comprised of foils with opposite end faces provided with solderable contact layers and having a metallic component in the form of a cap associated therewith. Each metal component is a separately manufactured element consisting of solder-resistant material and having at least one opening in a base region thereof, so that a solder connection extending at least into the opening between a connection layer and the metal component is formed. This embodiment assumes that, when installation on a printed circuit board is undertaken, the liquid solder reaches only the metal component, but not the actual capacitor. In the normal mounting and attachment of such chip components to printed circuit boards, however, the so-called flow solder method is employed wherein the components come virtually entirely into contact with liquid solder at a temperature of 260.degree. C. for approximately 10 seconds. This is particularly true if the components are arranged on the wiring side of the circuit board.